So, I was searching for a headphone amp for what seems like four years. With so much stuff coming out in the past decade the options have become near ludicrous. My needs were "fairly" simple: Neutral sound signature, class A circuit topology and the one aspect that kept me waiting so long, fully differential in and out, meaning a true balanced signal from input to my headphones. I heard about this little amp about two years ago and put off buying it until now.
The build of this amp is as solid as it is sturdy(oh my God I fear for that tiny gain switch) and well vented as this little thing could adequately heat a drink sitting on the top plate. The volume is not indicated well in low light, but using the volume knob itself feels like a quality volume pot, so smooth and linear. My DAC is also a recently purchased SMSL SU-8 which includes balanced outs and a dynamic range of 120 db with a respectable SNR of 116 db. I have only driven my headphones through the single ended output as I am saving again to buy balanced cables for each set I have: HD 600, HD800 and M1060. With the DAC and amp paired together via xlr cables, the overall noise floor is virtually undetectable. Dead silent. Not even the highly sensitive HD 800 can be heard over this pairing.
Here comes the honesty. Normally, I have driven my headphones out of my vintage receiver. The benefit of doing that was I had all the power to drive the M1060's with a built in graphic equalizer to help tame the treble on the HD 800's. My receiver also has a loudness control feature which basically amplifies the lowest and highest frequencies, to my ears, about 8-10 db. When this is off and the equalizer is leveled out the sound is dead neutral. Upon listening to my first set of tracks on the HPA-3B I noticed the amount of bass was on par with the receiver with the aforementioned features turned off. The bass is lean overall but present. The midrange, to me, sounds forward and at times a bit shouty but is smooth and resolving with the right music. Treble decay is airy and natural but more so when compared to my receiver. Class A topology allows for that extra bit of fidelity that class A/B(the receiver) just can't reach.
I use foobar2000 with an equalizer(when you own HD 800's or you're a nit picker in general it's a must) and so far I'd say the dac and amp sound great together. Until I get some balanced cables I can only enjoy single ended for now. I hope to add some updates in the future.